You are what you eat: describing the foraging ecology of southern elephant seals (Mirounga leonina) using blubber fatty acids

Abstract

Understanding the trophodynamics of marine ecosystems requires data on the temporal and spatial variation in predator diet but, particularly for wide-ranging species, these data are often unavailable. The southern elephant seal (Mirounga leonina) consumes large quantities of fish and squid prey in the Southern Ocean relative to other marine mammals; however, how diet varies relative to seasonal and spatial foraging behaviour is unknown. We used fatty acid (FA) signature analysis of 63 blubber cores from adult female M. leonina over three seasons (winter 1999, summer 2000 and winter 2001) to determine diet structure. We detected significant differences between seasons and between the main foraging regions (Antarctic continental shelf versus pelagic). We used the FA profiles from 53 fish, squid and krill species to construct a discriminant function that would classify each seal, from its blubber sample as having a fish-or squid-FA profile. We determined that a higher proportion of M. leonina had fish-dominated diets during the winter and when foraging around the Antarctic continental shelf, and the majority had more squiddominated diets during the summer when foraging pelagically. Thus, we were able to measure the coarsescale diet structure of a major marine predator using FA profiles, and estimate its associated seasonal and temporal variation.

Transfer of fatty acids from mothers to their calves during lactation in white whales Delphinapterus leucas

“…Some studies suggest that the deposition of the dietary lipids into the blubber layer is achieved in a very conservative manner, more or less without alteration, and consequently that the fatty-acid (FA) composition of the blubber of marine mammals can be used to identify the diet from both a qualitatively and quantitatively perspective (e.g. Iverson et al 1997, Hooker et al 2001, Bradshaw et al 2003. However, to date there is little direct evidence for the validity of this method for determining diet compositions (Grahl-Nielsen et al 2004).…”

Assessing the Functional Limitations of Lipids and Fatty Acids for Diet Determination: The Importance of Tissue Type, Quantity, and Quality

“…More recently, there has been a growing number of studies moving from traditional stomach-content analysis, which may provide a potentially limited view due to differences in digestibility among prey species (Hyslop, 1980), to time-integrated biochemical methods (reviewed in Traugott et al, 2013;Pethybridge et al, 2018). Lipid and fatty acid (FA) analysis is one such method growing in popularity as it has the capacity to elucidate key biological and ecological aspects, such as an organism's physiology and bioenergetics (Parrish et al, 2007;Pond and Tarling, 2011), and most often, trophic relationships (e.g., Bradshaw et al, 2003;Iverson et al, 2004;Budge et al, 2006). As per the saying "you are what you eat, " certain FAs are transferred from prey to predator with minimal modification (Iverson et al, 2004;Budge et al, 2006), allowing certain functional trophic groups to be traced within a food chain.…”

Variations in behavior and condition of a Southern Ocean top predator in relation to in situ oceanographic conditions

“…Because of their long migrations, stomach contents are almost entirely digested by the time seals return to land where prey remains can be studied. Cephalopods (squid and octopus) probably constitute their main diet (19)(20)(21), but new methods for diet study suggest that fish may, at least seasonally, make up a significant proportion (22). The spatial and vertical distribution of potential prey species is also poorly understood, especially during the winter season.…”